1. Field of the Invention
The present invention relates to a suspension for disc drive incorporated in an information processor, such as a personal computer.
2. Description of the Related Art
A hard disc drive (HDD) for writing and reading information to and from a rotating magnetic disc has a carriage that is turnable around an axis. The carriage is turned around the axis by a positioning motor. A carriage for disc drive described in Jpn. Pat. Appln. KOKAI Publication No. 2004-296072 has an actuator arm and a suspension on the distal end portion of the arm. The suspension is provided with a base plate, a load beam, a flexure, etc. A head including a slider is disposed on the distal end portion of the suspension. The slider is mounted on a tongue portion of the flexure.
When the disc rotates, the slider is caused to fly slightly above a surface of the disc by the pressure of air that flows between the disc surface and the slider. Thereupon, an air bearing is formed between the disc and the slider.
FIGS. 9 and 10 typically show a conventional suspension 1. The suspension 1 comprises a load beam 2 and a slider 4 mounted on a tongue portion 3 (shown in FIG. 10) of a flexure. When a disc 5 rotates at high speed in the direction of arrow R, air flows between the disc 5 and the slider 4, thereby forming an air bearing 6. An air inflow end and an air outflow end of the slider 4 are referred to as the leading side and the trailing side, respectively, in the art.
A dimple 7 is formed near the distal end of the load beam 2. The dimple 7 is a substantially hemispherical protuberance, which projects toward the slider 4. The slider 4 is swingable in a pitch direction and a roll direction around the dimple 7. An effective length L of the load beam 2 varies. Recently, there has been a trend toward a shorter load beam 2′ of, for example, 8.5 or 7 mm to replace a conventional load beam of, e.g., 12 mm.
As shown in FIG. 10, a read/write element 8 is provided on an end portion of the slider 4 on the trailing side. The distance from the trailing-side end portion of the slider 4 to the disc 5 is called a flying height (FH). A load F produced by a spring force that corresponds to deflection of the suspension 1 acts on the flying slider 4 through the dimple 7. At the same time, a leading-side reaction force P1 and a trailing-side reaction force P2 are produced by an air pressure of the air bearing 6. In order to stabilize the flying characteristics of the slider 4, moreover, a contrivance is made to generate a negative pressure P3. The negative pressure P3 is generated by recesses, e.g., shallow and deep etches, formed in a surface of the slider 4 by etching or the like.
Due to a mounting error of the suspension 1 on an arm (actuator arm), the mounting height (Z-height shown in FIG. 9) of the suspension 1 changes inevitably. If the Z-height changes, the deflection of the suspension 1 changes, so that the load F changes naturally. If the Z-height increases (or changes to the positive side), the deflection of the suspension 1 is reduced, so that the load F lessens. If the Z-height is reduced (or changes to the negative side), in contrast with this, the deflection of the suspension 1 increases, so that the load F increases.
In connection with the Z-height position of a suspension, in general, the pitch-direction tilt of the slider with the tongue portion in a free state is called a pitch static attitude (PSA). If the Z-height changes, the PSA also changes. If the Z-height increases, for example, the PSA also increases. If the Z-height is reduced, the PSA is also reduced. If the dimple position is in the center of the slider (central position with respect to the longitudinal direction), the product of the PSA and pitch stiffness represents a pitch moment. The pitch moment influences a flying pitch β (shown in FIG. 10) and also considerably influences the load and the flying height. According to an air bearing design for a modern slider, in particular, flying height sensitivity to the PSA is made higher than to the load, in order to reduce the influence of the flying height on the altitude above sea level (atmospheric concentration).
Usually, the dimple 7 is formed in the center (gravity center position with respect to the longitudinal direction) of the slider 4. However, a suspension may be designed such that the position of the dimple 7 is shifted to the leading side for a certain purpose.
FIG. 11 shows results of analysis of changes of the load F, leading-side force, and trailing-side force observed when the Z-height is changed in the suspension with its dimple shifted by 0.1 mm to the leading side. As shown in FIG. 11, the load F is reduced if the Z-height is changed from the negative side to the positive side. As this is done, both the leading- and trailing-side forces are reduced. In this case, the reduction of the leading-side force is greater than that of the trailing-side force. Therefore, the pitch moment changes, thereby causing the flying pitch (pitch-direction tilt β of the slider shown in FIG. 10) to change. The following is a qualitative description of this phenomenon.
FIG. 12 shows change of the attitude of the slider 4 obtained when the Z-height is increased in the suspension with its dimple shifted to the leading side.
As the Z-height is increased, in the example of FIG. 12, the PSA increases, so that a pitch moment M2 is generated. Besides, the load F that is reduced by the increase of the Z-height acts on the position that is shifted to the leading side. Therefore, a pitch moment M1 that is in the same direction as the increase of the PSA acts on the center of the slider 4. Thus, the increase of the flying pitch is promoted, so that the flying height (FH) is further reduced.
FIG. 13 shows change of the attitude of the slider 4 obtained when the Z-height is reduced in the suspension. As the Z-height is reduced, in this example, the PSA is reduced, so that a pitch moment M4 is generated. Besides, the load F that is increased by the reduction of the Z-height acts on the position that is shifted to the leading side. Therefore, a pitch moment M3 that is in the same direction as the reduction of the PSA acts on the center of the slider 4. Thus, the reduction of the flying pitch is promoted, so that the flying height (FH) is further increased.
For the reason described above, the sensitivity of the PSA to the Z-height increases in the shift amount with the dimple shifted to the leading side. In this case, the flying height is considerably dispersed by only a small change of the Z-height, so that it is difficult to decrease the flying height.
The shorter an effective length L (shown in FIG. 9) of the load beam, the more conspicuous the above problem is. This is because the load beam 2′ with a shorter effective length L, as compared with the load beam 2 with a longer effective length L, is configured so that its angle α changes more sharply as the Z-height changes, and the change of the PSA increases correspondingly. In the load beam 2′ with the shorter effective length L, therefore, the sensitivity of the PSA to the Z-height is further enhanced, so that it is more difficult to decrease the flying height.